DMR Lobster Surveys Indicate Strong Numbers but a Decline in Juvenile Settlement

DMR staff provided a comprehensive review of lobster research and recent landings during a session at the Maine Fishermen’s Forum. Department of Marine Resources (DMR) Commissioner Patrick Keliher announced the much anticipated news about 2017 lobster landings. As expected, lobster landings in 2017 came in lower, at 110.8 million pounds, with a value of $433.8 million. The 2017 lobster landings represent a drop of 16% from the previous year. According to DMR lobster biologist Kathleen Reardon, the summer months made a real difference in the 2016 versus 2017 lobster season. “Things changed in the summer . June and July were different,” she said. In both 2012 and 2016, June and July saw a spike in lobster landings, due to warmer-than-usual water temperatures in those years. The Maine lobster industry is fortunate to have several research programs dedicated to monitoring the health of the lobster resource. These programs monitor the various life stages of lobster from newly settled to juvenile to adult lobsters, providing critical insight on the resource before it reaches legal size. DMR biologist Robert Russell explained that juvenile lobster settlement was once again down in the 40 sites sampled by DMR. “It is the fourth year that settlement is below average, but it is not far off from the long-term average,” he said. Russell pointed out that juvenile lobsters are highly sensitive to water temperature when they reach settlement stage. The optimum temperature is 54oF. Thus in years when the coastal waters remain cool, such as 2017, there is less time for them to settle. In addition, lobsters sampled in the settlement surveys fall between 6.1 to 11.7 mm in carapace size. If the survey included slightly larger lobsters, up to 14.8 mm, then there would be more young of the year counted, making the survey numbers higher. Kathleen Thompson, director of DMR’s sea sampling program, spoke about the results of DMR’s 2017 surveys. The majority of the lobsters sampled during sea sampling are sublegal size. “The catch of sublegals per trap went way up in 2017, except for Zone F,” she noted. DMR’s ventless trap survey, conducted in June, July, and August, is designed to trap juvenile lobsters in coastal waters. The number of sublegal lobsters found in ventless traps in 2017 was less than in 2016, when coastal water temperatures were warmer. However, she found that sublegal lobsters had increased in the traps set in deeper water in eastern Maine. DMR’s spring and fall trawl surveys provide data not only on lobsters but many other commercially valuable species along the coast. The trawl surveys and the sea sampling surveys show a similar trend over time, Reardon noted, which was that sublegal size lobsters, those between 53 and 82 mm, were a dominant portion of the samples. The question that puzzles biologists is how to reconcile the low settlement numbers with the high volume of landed lobsters. “There’s a tremendous disconnect between egg production and the downturn in settlement,” Rick Wahle, University of Maine research professor, said. Egg production is at an all time high, yet settlement numbers have declined. The drop in settlement might be due to increased predation of larval lobsters, he argued, or it could be an expansion in nursery habitat due to warming waters making juvenile lobster density at sampling sites lower. Lobster larvae move through four stages of development before they make their way to bottom to settle at stage 4. “So what’s happening to them between stage 1 and 4?” Wahle asked. One factor that might explain the drop is the shift in copepod abundance, particularly Calanus finmarchicus, a fat-rich copepod that is also the preferred food of right whales. “If that is down, it affects larval abundance,” Wahle said. “Larvae might also be in different places due to the warming ocean.” Wahle is collaborating with Downeast lobstermen to set sampling traps in deep water to assess potential new lobster settlement in those areas. The intent is to understand better whether the surge in small lobsters in the historically cold eastern and deeper parts of the Gulf of Maine is the result of expanded settlement or whether juvenile lobsters are settling in shallow areas and then moving into deeper water. Andy Pershing, chief scientific officer and head of the Ecosystem Modeling Lab at the Gulf of Maine Research Institute (GMRI) in Portland, spoke about the GMRI computer model of the lobster population. The model is based on ocean climate data as well as lobster landings data. “GMRI models the whole life cycle of the lobster including reproduction. It is less data-dependent on the fishery,” Pershing explained. The model incorporates global climate data from the past 30 years as well as other variables like conservation practices in the lobster fishery and mortality from shell disease. The model indicated that, during this 30-year period, the Gulf of Maine lobster population increased by 515%, while the southern New England population declined by 78%. It forecasts that in the future, based on three different temperature scenarios in the Gulf of Maine, the lobster population will enter a gentle decline. “It assumes that conservation measures stay the same and harvesting effort stays the same,” Pershing said.